It has long been known in the disposable absorbent bandage art that it is extremely desirable to construct absorptive devices, such as disposable diapers, sanitary napkins, incontinent devices, absorbent wound dressings, and the like, presenting a soft, cloth-like surface feel to the user's skin at any anticipated points of contact, e.g., as fluid pervious topsheets and/or fluid-impervious backsheets.
While woven and non-woven fibrous webs are often employed in situations where fluid must be transmitted through the web because of their pleasant surface feel, polymeric webs comprised of plastic film have been shown to exhibit more desirable fluid transport and fluid restraining characteristics in many circumstances.
The use of fluid pervious polymeric webs as topsheets is well known in the art. For example, U.S. Pat. No. 3,814,101 issued to Kozak on June 4, 1974, suggests the use of a fluid pervious hydrophobic film provided with a plurality of valvular slits which restrict the reverse flow of liquid from the absorbent element of the device as a topsheet for a disposable absorbent bandage.
Commonly assigned U.S. Pat. No. 3,929,135 issued to Thompson on Dec. 30, 1975, discloses an exemplary prior art fluid pervious, macroscopically expanded three-dimensional topsheet comprised of liquid impermeable material, but provided with tapered capillaries, said capillaries having a base opening in the plane of the topsheet and an apex opening remote from the plane of the topsheet, said apex opening being in intimate contact with the absorbent pad utilized in the disposable absorbent bandage.
For the purpose of interpreting the present specification and claims, the term "macroscopically expanded", when used to describe three-dimensional plastic webs, ribbons and films of the present invention, refers to webs, ribbons and films which have been caused to conform to the surface of a three-dimensional forming structure so that both surfaces thereof exhibit a three-dimensional pattern of surface aberrations corresponding to the macroscopic cross-section of said forming structure, the surface aberrations comprising said pattern being individually discernible to the normal naked eye when the perpendicular distance between the viewer's eye and the plane of the web is about 12 inches. Such macroscopically expanded webs, ribbons and films are typically caused to conform to the surface of said forming structure by embossing, i.e., when the forming structure exhibits a pattern comprised primarily of male projections, by debossing, i.e., when the forming structure exhibits a pattern comprised primarily of female capillary networks, or by extrusion of a resinous melt directly onto the surface of a forming structue of either type. Also for the purpose of interpreting the present specification and claims, the term "planar", when utilized herein to describe plastic webs, ribbons and films of the present invention, refers to the overall condition of the web, ribbon or film when viewed by the normal naked eye on a macroscopic scale. In this context "planar" webs, ribbons and films may include webs, ribbons and films having a fine scale, yet visible, pattern of surface aberrations on one or both sides thereof, the surface aberrations comprising said visible pattern not being individually discernible to the normal naked eye when the perpendicular distance between the viewer's eye and the plane of the web is about 12 inches.
Macroscopically expanded polymeric webs employing features to reduce gloss and improve tactile impression are also disclosed in the prior art, as is the use of such webs as topsheets and/or backsheets in disposable absorbent bandages. For example, commonly assigned U.S. Pat. No. 4,327,730 issued to Sorensen on May 4, 1982 discloses a disposable diaper having a fluid pervious textured topsheet of thermoplastic material. The topsheet is macroscopically expanded and is provided with a multiplicity of nubbles across its surface. The nubbles do not substantially alter the macroscopic profile of the film, but do impart a more cloth-like tactile impression and reduced gloss to the film.
Another macroscopically expanded three-dimensional polymeric web exhibiting a substantially non-glossy visible surface and cloth-like tactile impression is disclosed in commonly assigned U.S. Pat. No. 4,463,045 issued to Ahr et al. on July 31, 1984. The visible surface of the macroscopically expanded three-dimensional polymeric web of Ahr et al. is preferably provided with a regularly spaced, microscopic pattern of surface aberrations, said pattern being too fine to be discernible by the normal naked eye when the perpendicular distance between the viewer's eye and the plane of the web is about 12 inches, but which pattern of surface aberrations is highly effective in substantially eliminating specular reflection of incident light. The non-glossy surface of the web exhibits substantially no planar areas which are large enough to inscribe a four (4) mil diameter circle. Said webs may be produced by means of a one-sided forming process wherein said surface aberrations are transmitted through the thickness of the web during processing or by means of a two-sided forming process wherein said surface aberrations are imposed directly onto the visible surface of the web. The surface aberrations may comprise either protuberances projecting generally outwardly from the surface of the web or depressions projecting generally inwardly from the surface of the web, e.g., the knuckle pattern of a fine woven wire embossing member. Macroscopically expanded three-dimensional polymeric webs of the type disclosed in the patent to Ahr et al. are often employed as alternatives for cloth and fiber structures which contact the wearer's skin.
The commonly assigned patent to Ahr et al. teaches the criteria which must be met with respect to the regularly spaced pattern of surface aberrations in order to diffusely reflect incident light and thereby eliminate gloss. It further teaches that in those situations where a more cloth-like or fiber-like tactile impression in the resultant macroscopically expanded three-dimensonal plastic web is also desired, the surface aberrations in the web should preferably exhibit an average amplitude of at least about 0.2 mils (i.e., 0.0002 inches), and most preferably at least about 0.3 mils (i.e., 0.0003 inches). According to Ahr et al., a more cloth-like or fiber-like tactile impression is perceived in macroscopically expanded three-dimensional plastic webs which meet the aforementioned amplitude criteria whether the surface aberrations comprise protuberances or depressions due to the fact that in either case the surface of the web is divided into at least two distinct planes separated from one another by a distance of at least 0.2 mils (i.e., 0.0002 inches). Ahr et al. further teach that in the case of protuberances, it is the tops of the aberrations which contact the observer's skin, while in the case of depressions it is the substantially planar surface in which said aberrations originate which contacts the observer's skin. Because said division is carried out in a fine microscopic pattern, only the reduced area of contact with the uppermost surface of the web and not existence of the pattern is tactually perceived.
Because of the superior fluid and vapor handling characteristics which can be provided in polymeric webs of the aforementioned type and their inherent cost advantages when contrasted to woven and non-woven fibrous webs, considerable developmental effort has been expended by manufacturers of disposable absorbent bandages to improve the consumer's reaction to placing polymeric webs in contact with the skin. Indeed, much technological progress has been made toward eliminating the negative consumer reaction to placing polymeric webs comprised of plastic film in contact with the user's skin, particularly in the context of a wearer-contacting topsheet. See, for example, commonly assigned U.S. Pat. No. 4,342,314 issued to Radel et al. on Aug. 3, 1982, the aforementioned commonly assigned U.S. patent to Ahr et al. and commonly assigned U.S. Pat. No. 4,637,819 issued to Ouellette et al. on Jan. 20, 1987, all of said commonly assigned U.S. patents being hereby incorporated herein by reference. By comparison, relatively little attention has been specifically focused on improving the charcteristics of polymeric webs when they are used as a fluid-impervious backsheet in a disposable absorbent bandage structure.
U.S. Pat. No. 3,911,187 issued to Raley on Oct. 7, 1975 discloses a typical prior art fluid-impervious thermoplastic film used as a backsheet in structures such as disposable absorbent bandages, said film having a permanently embossed design which allegedly simulates woven fabric or cloth and which has edge curl resistance under machine stress. The embossed design is made up of latitudinally and longitudinally alternating hollow protuberances and depressions on both sides of the film. The width of the protuberances at their base varies from about 5 mils to about 50 mils, most preferably from about 5 mils to about 20 mils. In the disclosed embodiment, the protuberances are comprised of a multiplicity of planar wall segments.
U.S. Pat. No. 4,343,848 issued to Leonard, Jr. on Aug. 10, 1982 discloses another prior art fluid-impervious embossed thermoplastic film used as a backsheet, said film being characterized in that one surface thereof is provided with a plurality of rows of protuberances having the shape of pyramids with square bases which extend perpendicular to both the longitudinal and the transverse axes of the film. The protuberances are joined at the edge of the bases by flat valley portions which intersect each other at right angles. It is alleged that the embossed film has a low coefficient of friction and increased embossed thickness. The protuberances in the disclosed embodiment preferably have a base from about 4 mils to about 10 mils and a height from about 1/2 mil to about 4 mils. In the disclosed embodiment, the pyramids are comprised of substantially planar wall segments.
U.S. Pat. No. 3,484,835 issued to Trounstine on Dec. 16, 1969 discloses still another prior art fluid-impervious plastic film which allegedly simulates a plain woven fabric or cloth and which has edge-curl resistance under machine stress. The film is characterized as possessing a series of raised bosses, separated by substantially perpendicularly intersecting longitudinal and lateral channel-like areas on the top side of the film, said channel-like areas being spaced apart about 0.010 inch to form a network of generally rectangular-shaped channels separating the raised bosses, said raised bosses protruding above the channel-like areas to a height in the range of about 0.003 to about 0.004 inches.
U.S. Pat. No. 3,724,673 issued to Ryon on Apr. 3, 1973 discloses still another textured thin polymeric membrane. In particular, Ryon discloses a polymeric film comprised of thermoplastic material and having a myriad of thermoplastically formed deformations in which the film which defines the deformations is at least in part thinner than the film between said deformations. The deformations prevent cohesion between adjacent membranes without causing a reduction in oxygen transport capability when a plurality of membranes are utilized in fluid exchange devices such as blood oxygenators and dialyzers.
U.S. Pat. No. 4,132,594 issued to Bank et al. on Jan. 2, 1979 disclose a gas diffusion liquid storage bag wherein a blood bag made of medical grade plastic is made with a multiplicity of regions thin enought to permit a desired rate of diffusion therethrough of CO.sub.2, yet which has thick or otherwise sufficiently reinforced regions to provide handling strength for the bag.
From the foregoing it is clear that fluid-impervious polymeric webs are very well known in the art. It is also clear that many artisans have employed prior art fluid-impervious polymeric webs as backsheets on disposable absorbent garments such as diapers and incontinence devices.
However, a major disadvantage of the prior art fluid-impervious webs which have to this point been used as backsheets on such structures is that they are "noisy" when worn, i.e., "rattling" or "rustling" sounds caused by the wearer's body movements may betray the fact that a protective garment is being worn. While this is not often a concern where infant garments are involved, adult incontinence devices are now finding widespread acceptance amongst persons unable to control their normal bodily discharges. To individuals afflicted with this problem, the "rattling" or "rustling" sounds often generated by body movement when wearing garments employing such prior art liquid-impervious backsheets can be extremely embarrassing.
For many years it was believed that these "rattling" or "rustling" sounds were simply an inherent characteristic of polymeric webs. However, commonly assigned U.S. Pat. No. 4,629,643 issued to Curro et al. on Dec. 16, 1986 teaches a way of providing a plastic film which not only exhibits a highly desirable soft and silky tactile impression, but which, in addition, is extremely effective in reducing the "noises" which normally result when plastic webs are employed in disposable absorbent bandage structures. Unfortunately, plastic webs of the type disclosed in the aforementioned commonly assigned U.S. patent to Curro et al. are microapertured, i.e., they exhibit a fine scale pattern of surface aberrations which end in volcano-like apertures at their points of maximum amplitude. They are not by themselves suitable for use as backsheets, since they are not impervious to fluid.
One solution to providing a backsheet which exhibits the highly desirable soft and silky tactile impression of microapertured webs of the type disclosed in the aforementioned commonly assigned U.S. Patent to Curro et al., yet which is impervious to the passage of fluid, is disclosed in the commonly assigned, allowed U.S. Patent Application of E. Kelly Linman, John Joseph Curro and Eugene Weinshenker, U.S. patent application Ser. No. 740,084, filed on May 31, 1985 and entitled NON-OCCLUDING, LIQUID-IMPERVIOUS BACKSHEET FOR ABSORPTIVE DEVICES.
The latter commonly assigned U.S. Patent Application of Linman, Curro and Weinshenker discloses a backsheet comprising a combination of two layers. The first layer, which does not contact the wearer's skin, is preferably comprised of a fluid-impervious layer of polymeric film or the like. The second layer, which is also preferably comprised of a polymeric film, is pervious to both gas and fluid by virtue of a fine scale pattern of relatively small surface aberrations, each ending in a volcano-like aperture at its apex. The web comprising the second layer is preferably produced in accordance with the teachings of the aforementioned commonly assigned U.S. Pat. No. 4,629,643 to Curro et al. The second layer is preferably oriented so that the tiny volcano-like cusps of the surface aberrations constitute the exposed portion of the backsheet. This minimizes the surface area of the web in contact with the wearer's skin at any points of contact between the backsheet and the wearer's skin. In addition, the tiny apertures in the second layer substantially prevent occlusion of the wearer's skin by permitting air to circulate between the first fluid-impervius layer of the composite backsheet and the wearer's skin through the tiny apertures in the second layer. This effect is enhanced even further when the first microapertured layer is macroscopically expanded to enhance the amount of stand-off between the wearer's skin and the fluid-impervious first layer.
While the fluid-impervious composite backsheet disclosed in the commonly assigned U.S. Patent Application of Linman, Curro and Weinshenker does represent a significant advance over prior art single layer plastic backsheets in the areas of improved visual and tactile impression and avoidance of skin occlusion at points of contact between the backsheet and the wearer's skin, it normally increases the cost of products on which it is employed due to the fact it comprises two layers of material rather than one. In addition, it has been observed that while composite backsheets of the type disclosed in the commonly assigned U.S. Patent Application of Linman, Curro and Weinshenker are in most instances less "noisy" than prior art single layer plastic backsheets, they are still not as "quiet" as the microapertured webs disclosed in commonly assigned U.S. Pat. No. 4,629,623 to Curro et al. when the microapertured webs are employed by themselves.